The present invention relates to marine propulsion devices, and more particularly to a transom extension mounting assembly for an outboard motor.
Marine propulsion devices such as outboard motors are supported from a boat transom by a motor mounting assembly. Various types of motor mounting assemblies are known, as for example a transom bracket for mounting the outboard motor directly on a boat transom. While the motor may be trimmed when mounted on a transom bracket, the motor's vertical height cannot be changed. Therefore, the outboard motor is typically mounted at a comprising position at a fixed height which will provide the best possible overall performance. Another type of motor mounting assembly relates to one which is capable of selectively supporting an outboard motor in either raised or lowered positions wholly aft of the boat transom. Many of these latter transom extension types of mounting assemblies are of the general type which include a parallelogram linkage.
Recently, transom extension mounting assemblies have become increasingly popular on high performance outboard motor powered boats including bass boats where a lower position of the motor improves initial boat acceleration, and a higher position enhances top speed by reducing gear case drag and reducing draft for shallow water operation. It is further known that relocating the motor aft of the transom improves the handling characteristics of most boats at high speeds. These devices also allow the boat to have a higher transom for improved safety in following-wave conditions and they allow boat builders to manufacture a common hull/transom design for both outboard and stern drive applications.
Examples of outboard motor mounting assemblies which support the outboard motor wholly aft of the boat transom are disclosed in the following United States patents:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 2,737,920 Heath 1956 2,782,744 Staley 1957 3,990,660 Pipoz 1976 4,013,249 Meyer et al 1977 4,168,818 Ellis 1979 4,306,703 Finze 1981 4,354,848 Hall et al 1982 4,363,629 Hall et al 1982 4,367,860 Strang 1983 4,384,856 Hall et al 1983 4,406,632 Blanchard 1983 4,406,634 Blanchard 1983 4,482,332 Emmons 1984 4,504,237 Blanchard 1985 ______________________________________
One limitation of a parallelogram linkage arrangement is that the outboard motor is raised and lowered along a substantially vertical plane. This results in a horizontal thrust plane throughout the full movement of the outboard motor between its raised and lowered positions. Thus, for example, when the outboard motor is in its fully lowered position and the boat is accelerated rapidly the front of the boat becomes elevated or raised out of the water which results in the propeller axis or thrust plane angled upwardly with respect to a horizontal plane, i.e. the water surface, instead of being parallel to the water surface which would provide maximum thrust and speed. Ideally therefore the outboard motor should be orientated so that its thrust plane is parallel with respect to a horizontal plane, such as the water surface, regardless of whether the boat is accelerating or cruising. Additionally, it is desirable to be able 5 to move the outboard motor between a lowered position, which is advantageous for acceleration purposes, and a plurality of raised positions which are advantageous for cruising purposes under varying load and water conditions. Such optimum orientations would aid in providing maximum thrust and speed resulting in maximum efficiency and performance from the outboard motor.